1. Field of the Invention
The present invention relates to reagents and methods for releasing and measuring lead in blood.
2. Background Discussion
Lead and its compounds have become widely distributed in the environment over the centuries. Lead is known to be toxic and have deleterious effects on humans. The toxicity of lead is well documented. Trace amounts of lead can adversely affect the function of various organs of the human body, especially in small children. It is now generally recognized that lead poisoning occurs at blood levels as low as 10 to 15 .mu.g/dL. Thus, the detection and measurement of lead in blood is extremely important in providing universal blood screening and in monitoring occupational lead exposure.
Most lead screening programs use atomic absorption or anodic stripping voltametry methods for the determination of trace amounts of lead. Both methods are cumbersome to use, susceptible to contamination, and costly. Enzyme-based biodetection systems of lead, which employ .delta.-aminolevulinic acid dehydrase (ALAD) and isocitrate dehydrogenase, have also been proposed. An automated fluorimetric lead assay, which uses inhibition of ALAD by lead is disclosed in PTC International Publication No. W095/17679 to Wong et al., which discloses the detection of lead in a sample by adding a lead recovery agent to an assay solution containing lead, adding a disulfide enzyme to the assay solution and correlating the activity of the disulfide enzyme to the amount of lead in the sample.
The Wong et al. patent discloses the use of acids such as trichloroacetic acid, nitric acid, 5-sulfosalicylic acid, or perchloric acid as an initial treatment step in separating lead ions from a blood sample. However, the resulting lead-containing aqueous supernatant must be neutralized with a buffer containing a lead recovery agent before analysis. Otherwise, the lead is unavailable for measurement.
Other methods of sample pretreatment include acid digestion or dilution of blood with a matrix modifier such as a nitric acid solution of ammonium phosphate and a nonionic surfactant, prior to analysis by atomic absorption.